1. Field of the Invention
The present invention relates to a belt pressing mechanism employing an improved elastic device for a constant-horsepower transmission capable of frictionally transmitting power and used in industrial machines, such as machine tools, vehicles, motors, generators and the like. More particularly, the present invention relates to a belt pressing mechanism suitable for high-load power transmission, capable of stabilizing the transmission of high pressure produced by a compressed elastic device through a pulley to a belt, and of extending the life of the belt by suppressing the high-pressure deterioration of transmission members including elastic members and a belt.
1. Description of the Related Art
Various devices having a secondary pulley combined with an elastic member, and a primary pulley not combined with any elastic member are disclosed in Japanese Patent No. 1,624,499 and U.S. Pat. Nos. 5,334,103 and 5,567,094 and have been put on the market. The power output characteristic of the secondary pulley of such a device is capable of constant-torque power transmission and is incapable of constant-horsepower power transmission for the following reasons.
Power P (W) that is transmitted to a load is expressed by:
P=1.027xc3x97Nxc3x97Txe2x80x83xe2x80x83(1)
where N (rpm) is rotating speed and T (kgxc2x7m) is torque.
When transmitting a required power P0, the torque T must be decreased when the rotating speed N is increased, and the torque T must be increased when the rotating speed N is decreased. The elastic member pressure controller based on the conventional technical idea increases the compressive pressure as the rotating speed increases and decreases the compressive pressure as the rotating speed decreases; that is, the pressure is directly proportional to the rotating speed. In a constant-horsepower transmission, the pressure must be inversely proportional to the rotating speed. Therefore, a belt transmission member pressing device employing an elastic member of this type is unable to produce a required frictional force and constant-horsepower transmission cannot be practiced in principle.
When practicing an idea expressed by Expression (1), high pressure causes problems in a range of low rotating speeds. A first problem is a fact that a transmission member deforms and deteriorates in a short period under high pressure and a second problem is a fact that the transmission member is incapable of absorbing shocks of high pressure and power transmission becomes unstable or impossible. Shocks are given to a frictional transmission surface of the transmission member and portions of the frictional transmission surface in point contact with the transmission member are damaged mechanically. A transmission belt is permanently elongated and the elastic member sets permanently and the length thereof is reduced permanently when kept under a high pressure for a long time. Since a predetermined frictional force cannot be applied to the transmission pulley by a simple pressure applying operation, the degree of mechanical damage in the members due to the application of an excessively high pressure or an excessively low pressure thereto increases and the power transmission becomes impossible. Therefore three measures must be taken for the transmission member to which high pressure is applied. The transmission mechanism must be capable of a shock absorbing function and an aligning function to avoid damaging, deforming and deteriorating component members. The transmission mechanism must be capable of avoiding causing and making serious the deterioration and deformation of the component members. The transmission mechanism must be capable of compensating for the deformation and deterioration of the component members. Those conditions relate to the operating principle of the transmission mechanism and the structural features of the transmission mechanism. When those conditions are satisfied, transmission control operation can be stabilized and the life of the transmission mechanism can be extended.
Accordingly, it is a general object of the present invention to provide a belt pressing mechanism for a continuously variable transmission, capable of assuring a self-adjusting or automatic aligning function of one of two pulleys for constant-horsepower transmission to determine a stable position for a belt extended between the two pulleys by applying an elastic pressure corresponding to a normal pressure to the friction surface of the pulley and by making the simultaneous pressure application by the two pulleys or the independent pressure application by the elastic force applying pulley controllable to compensate for the deterioration of high-pressure members and to ensure long-term stable power transmission.
It is a first object of the present invention to extend the life of members subject to deterioration by providing a belt pressing mechanism capable of changing pressure in a low-pressure state in which deformation and deterioration are suppressed substantially as well as in a high-pressure state to maintain the stable frictional force of a high-pressure deteriorating member, such as an elastic member or a belt.
It is a second object of the present invention to provide a changing mechanism for selectively operating two pulleys in a variable speed operating mode in which the two pulleys are operated synchronously by a speed change instruction or in an individual pressure application mode in which pressure is applied only to an elastic force applying pulley by a pressure removal instruction to provide bases for various control modes.
It is a third object of the present invention to make possible synchronous change between the variable speed operating mode and the individual pressure application mode, to select a high-pressure state for a period in which the transmission is in operation or a low-pressure state for a period in which the transmission is not in operation, and to make the individual pressure application mode operate as a shaft torque control mode or a release pressure change mode.
It is a fourth object of the present invention to practice an automatic restoring and compensating function to restore an initial normal output rotating speed and output torque by compensating for deformation and deterioration of members caused by the application of high pressures for a long period of time or the repetitive application of high and low pressures by other means.
It is a fifth object of the present invention to practice not only a constant-horsepower transmission but also a constant torque, a single axial torque or a high pressure releasing operation by a pair of pressing functions comprising input and output pulleys operating independently as a reference pulley and a follower pulley irrespective of kinds of belts.
With the foregoing objects in view, a common means according to the present invention for solving the foregoing problems includes a driving means capable of selecting a variable speed operating condition or a non-variable speed operating condition and of applying pressure only to an elastic force applying pulley, and a pressure application controller capable of controlling individually the pressure force or the elastic force applying pulley in a variable-pressure control motion to ensure long-term stable transmission by giving a speed change instruction or a pressure removal instruction in the speed change operation or the non-variable speed operation.
According to a first aspect of the present invention, a means for solving the foregoing problems includes a driving means and a pressure application controller that set the elastic force applying pulley in a high-pressure state for frictional power transmission while the transmission is in a power transmitting operation or in a low-pressure state for suppressing the deformation and deterioration of an elastic member or a belt while the transmission is stopped.
According to a second aspect of the present invention, a means for solving the foregoing problems includes a first pressing device capable of controlling pressure applied to one of two pulleys, a second pressing device capable of controlling pressure applied to the other pulley, and a mode change controller for controlling the first and the second pressing device for synchronous or asynchronous operation according to instructions provided by pressure application controllers to select either a variable speed operating mode or an individual pressure application mode.
According to a third aspect of the present invention, a means for solving the foregoing problems includes a mode change controller for controlling operations for changing the two pulleys synchronously or asynchronously by the first and the second pressing device, and a pressure application controller for applying pressure to elastic members and/or a movable disc included in the pressing device for the elastic force applying pulley in an individual pressure application mode in a high-pressure state or a low-pressure state.
According to a fourth aspect of the present invention, a means for solving the foregoing problems estimates a deterioration error in a high-pressure deteriorated member from a measured rotating speed or a measured frictional force exerted by an output belt measured by a sensor, and a set rotating speed or a set frictional force stored in a processor, and adds a compensation value corresponding to the deterioration error to a speed change instructions or a pressure removal instruction given to the pressing devices to maintain a normal rotating speed and a normal frictional force.
According to a fifth aspect of the present invention, a controller provides an synchronous instruction for a first pressing device for applying an elastic pressure and a second pressing device for applying a non-elastic pressure thereto at the time of synchronous operation as a control instruction, and provides an asynchronous instruction at the time of asynchronous operation or an instruction to variably control only one of the pressing devices as a control instruction